i have had the problem several times
on and off for the last several months.
it might have to do with the size of the photo
or, for me at least, the number of photos.
i uploaded 5 pics just now
4 worked, and the 5th didnt
the pop-up window turns into a "compose" window.
the pic sizes that did upload were 2 to 4 meg... so, pretty large...
and, i have had problems with smaller ones
so, i dont think it has to do with size.